We configured the irule for the MQTT application and the irule was accepted but when we tried to assign it to VIP then it gave us the error mentioned in the below article.
There is not enough information here to help you - exactly which iRule, on exactly which virtual server. It is obviously throwing this error because of some issue in your configuration, so review your configuration and try to change it to see whether it works. The case you menation talks about iApps, this seems relevant. If you can't find the issue, raise a support case and provide a qkview.
